Instead of one server with a game loop and geographical control over one area—a server which can't take a lot of load or handle interesting behaviour—we have a swarm of processors that live and die as and when they're needed. These orchestrate together without a game loop, without a central controller, to model and simulate a world, and it just scales, because you have a swarm of these things.

Now, instead of a single game engine you have thousands of these workers that are able to collaborate on the fly, in milliseconds, to congregate within a space in the gameworld, and do work that simulates the world. We're able to siphon off different things, like physics, AI, whatever, to things that are very good at doing that kind of work. Instead of a central authoritative loop, which is how games and simulations are traditionally made, think of it as a big swarm or orchestra of processors.